The invention relates to a production machine of the kind described in the U.S. patent application 07/413076 of 09.27.1989 now abandoned, which will henceforth be called the "Initial Patent".
The Initial Patent notably describes a walking beam lift and carry device enabling palettes to be presented successively on different workstations. The system is mainly geared to automatic assembly, the palettes acting as support to the product being manufactured, and each workstation corresponding to an operation of the process to be performed (insertion, welding, crimping, checking, etc.). To this end, each station is equipped with a suitable device which will henceforth be designated by the general name "working module".
An essential feature of the type of machine thus achieved is a high degree of flexibility, obtained by equipping each module (lift and carry module and working modules) with individual motorization, synchronization being achieved by electronic control. This control, according to the different situations encountered, enables operating cycles to be set in motion at the level of each module, when this operation is possible and necessary, and enables the module to be left inactive in the opposite case.
Another feature of the machine lies in its linear configuration, which makes it particularly suitable for integration into a production line comprising other machines upline and downline, the link between the machines being easily able to be achieved by conveyor sections which may act a buffer stocks.
The flexibility of operation described in the foregoing paragraph can usefully be taken advantage of:
at the lift and carry module level to subordinate its operation to the fact that certain necessary conditions are correctly met:
upline feed (presence of a palette against the machine input stop)
no downline blocking (no accumulation beyond a certain critical point on the downline conveyor)
ability of the working modules to fulfill their function
at the working module level, to adapt the machine to the different versions of the product to be manufactured, by rendering such or such a module active or inactive depending on the version involved (the latter being automatically identified by reading of a coding at the machine input).
Thus described by the Initial Patent, a machine of this kind is suited to integration in a system with a strictly linear configuration, i.e. starting from an empty palette on which the product to be manufactured is progressively built up by successive operations. At the end of the process, the finished product is removed from the palette, which is then recycled back to the machine at the head of the line.
In pure theory, such a system could be achieved by a single machine presenting the required number of workstations. In practice, this number is generally such that several machines have to be placed in series linked by conveyor devices, as described above.
A linear system of this kind can be advantageously used whenever the range of operations to be carried out permits, which is not always the case. Certain constraints may in fact arise, notably in the assembly field, which cannot always be met by the linear configuration:
A product incorporating distinctly individualized sub-assemblies, each sub-assembly having to be subjected to a very specific process before being incorporated in the main product. The production line then becomes tree-structured (in the same way as the range), i.e. it is composed of a main line leading to the finished product, and of one or more branch lines, each of these lines being dedicated to a given sub-assembly.
The presence of operations which, for technical reasons, cannot be carried out on the palettes conveying the main product (for example, shaping or welding operations which absolutely must be performed before insertion in the main product for reasons of accessibility or pollution).
The object of the type of machine involved in the present invention is to solve the problems set out above. We will first of all examine the first one, and will see that the second one is no more than a particular case.
When a sub-assembly is manufactured on a branch line, the latter may be equipped with conventional machines, depending on the operations to be carried out. But it must end with a special machine, which is common with the main line, and whose essential function is to transfer the finished sub-assembly to the main product being manufactured. Such a machine will henceforth be designated "convergence station". On the main line, it can occupy any position (generally along the line, but it may be at the head or at the end of the line in certain cases). On the branch line, it must occupy the end-of-line position, i.e. the corresponding palettes leave it empty and are recycled to the machine at the head of the branch line.